Physiological active substances such as various hormones and neurotransmitters regulate the biological function via specific receptor proteins present on cell membranes. Many of these receptor proteins are coupled with guanine nucleotide-binding protein (hereinafter sometimes simply referred to as G protein) and mediate the intracellular signal transduction via activation of G protein. These receptor proteins possess the common structure containing seven transmembrane domains and are thus collectively referred to as G protein-coupled receptors or seven-transmembrane receptors (7TMR).
G protein-coupled receptor proteins are present on the cell surface of each functional cell and organ in the body, and play important physiological roles as the target of the molecules that regulate the functions of the cells and organs, e.g., hormones, neurotransmitters, physiologically active substances and the like. Receptors transmit signals to cells via binding with physiologically active substances, and the signals induce various reactions such as activation and inhibition of the cells.
To clarify the relationship between substances that regulate complex biological functions in various cells and organs, and their specific receptor proteins, in particular, G protein-coupled receptor proteins would elucidate the functional mechanisms in various cells and organs in the body to provide a very important means for development of drugs closely associated with the functions.
For example, in various organs, their physiological functions are controlled in vivo through regulation by many hormones, hormone-like substances, neurotransmitters or physiologically active substances. In particular, physiologically active substances are found in numerous sites of the body and regulate the physiological functions through their corresponding receptor proteins. Many unknown hormones, neurotransmitters or many other physiologically active substances still exist in the body and, as to their receptor proteins, many of these proteins have not yet been reported. In addition, it is still unknown if there are subtypes of known receptor proteins.
It is very important for development of drugs to clarify the relationship between substances that regulate elaborated functions in vivo and their specific receptor proteins. Furthermore, for efficient screening of agonists and antagonists to receptor proteins in development of drugs, it is required to clarify functional mechanisms of receptor protein genes expressed in vivo and express the genes in an appropriate expression system.
In recent years, random analysis of cDNA sequences has been actively studied as a means for analyzing genes expressed in vivo. The sequences of cDNA fragments thus obtained have been registered on and published to databases as Expressed Sequence Tag (EST). However, since many ESTs contain sequence information only, it is difficult to predict their functions from the information.
The amino acid sequence of human-derived GPR40 and the DNA encoding the same are reported (WO 2000-22129 and Biochem. Biophys. Res. Commun. 1997, Oct. 20; 239 (2): 543–547).
Also, it is reported that the ligand to human-derived GPR40 is a fatty acid (WO 02/057783).
Heretofore, substances that inhibit the binding of G protein-coupled proteins to physiologically active substances (i.e., ligands) and substances that bind and induce signals similar to those physiologically active substances (i.e., ligands) have been used for pharmaceuticals as antagonists and agonists specific to the receptors that regulate the biological functions. Therefore, these substances are not only important for physiological expression in the body as stated above but discovery and cloning of its gene (e.g., cDNA) for a novel G protein-coupled receptor that can be targeted for pharmaceutical development are also very important means in search for a specific ligand, agonist, and antagonist of the novel G protein-coupled receptor.
However, not all G protein-coupled receptors have been discovered. There are unknown G protein-coupled receptors and many of these receptors in which the corresponding ligands are yet unidentified are called orphan receptors. Therefore, search and functional elucidation of a novel G protein-coupled receptor is eagerly awaited.
G protein-coupled receptors are useful in searching for a novel physiological active substance (i.e., ligand) using the signal transduction activity as an indicator and in search for agonists and antagonists of the receptor. On the other hand, even if no physiological ligand is found, agonists and antagonist of the receptor may be prepared by analyzing the physiological action of the receptor through inactivation experiment of the receptor (knockout animal). Ligands, agonists, antagonists, etc. of the receptor are expected to be used as prophylactic/therapeutic and diagnostic agents for diseases associated with dysfunction of the G protein-coupled receptor.
Attenuation or accentuation in functions of the G protein coupled receptor due to genetic aberration of the G protein-coupled receptor protein in vivo causes some disorders in many cases. In this case, the G protein coupled receptor may be used not only for administration of antagonists or agonists of the receptor, but also for gene therapy by transfer of the receptor gene into the body (or some particular organs) or by introduction of the antisense nucleic acid of the receptor gene into the body (or the particular organ). In this case, information on the base sequence of the receptor gene is essentially required for investigating deletion or mutation in the gene. The receptor gene is also applicable as prophylactic/therapeutic and diagnostic agents for diseases associated with dysfunction of the receptor.
The present invention provides a novel and useful G protein-coupled receptor protein as described above. That is, the present invention provides a novel G protein-coupled receptor protein, its partial peptides and salts thereof; polynucleotides (DNA and RNA, and derivatives thereof) containing the polynucleotides (DNA and RNA, and derivatives thereof) encoding the G protein-coupled receptor protein or its partial peptides; recombinant vectors containing the polynucleotides; transformants bearing the recombinant vectors; methods for manufacturing the G protein-coupled receptor protein or its salts; antibodies to the G protein-coupled receptor protein, its partial peptides and salts thereof; compounds that change the expression level of said G protein-coupled receptor protein; methods of determining ligands to the G protein-coupled receptor protein; methods for screening the compounds (antagonists and agonists) or salts thereof that change the binding properties of ligands and the G protein-coupled receptor protein; kits for use in the screening methods, compounds (antagonists and agonists) or salts thereof that change the binding properties of ligands obtainable by the screening methods or obtainable using the screening kits and the G protein-coupled receptor protein, or pharmaceuticals comprising the compounds (antagonists and agonists) that change the binding properties of ligands to the G protein-coupled receptor protein, or compounds or salts thereof that change the expression level of the G protein-coupled receptor protein; etc.